Almost half of the energy expended by some semiconductor-based electronic apparatuses, such as silicon microchips, during their manufacture and lifetime is spent just to produce the semiconductor material, such as silicon wafer material. Another quarter is spent during the operating lifetime of the electronic apparatuses. Any technique that reduces the energy associated with fabrication of the semiconductor material, such as a silicon wafer, and power consumption during operation may reduce the overall cost of the apparatus, such as a silicon microchip integrated circuit. Silicon-on-insulator technology can result in lower power consumption and also increase the speed of operation of integrated circuits due to a reduction in stray capacitance.
A variety of techniques may be used to implement silicon-on-insulator (SOI) technology including, but not limited to, SIMOX (Separation by IMplantation of OXygen), SPIMOX (Separation by Plasma IMplantation of OXygen), SOS (Silicon-On-Sapphire), bonding silicon wafers on oxidized silicon wafers, and forming thin film polysilicon on a glass substrate, such as for thin film transistor (TFT) technology used in liquid crystal displays. Even so, the TFT technology in display applications is often of lower performance since the silicon material is not monocrystalline and has grain boundaries.
Although the bonded wafer technology may be preferred in certain circumstances, one problem with such technology is the difference in the coefficient of thermal expansion (CTE) between the bonded materials. For example, in the case of a silicon wafer having a CTE of 2.6×10−6 centimeters/(centimeters K) (cm/(cm K)) bonded to an oxidized silicon wafer having a CTE of 0.5×10−6 cm/(cm K) there is a sufficient mismatch of the CTE to produce excessive stress and exceed the strain limit of the materials. If the strain is too large, then the materials will plastically deform by the introduction of dislocations, fracture and yield, or excessive wafer bowing and/or warping. Some attempts have been made to bond silicon to compliant substrates using low viscosity borophosphosilicate glass films that flow to reduce the stress. However, such attempts have not produced satisfactory results.
Accordingly, a desire exists to bond semiconductive materials to an insulative substrate without introducing excessive stress.